The present invention relates to glass bubbles for use in fillers for plastic resin articles and, in particular, to glass compositions for those glass bubbles.
Glass bubbles or hollow glass spheres have been used as fillers in plastic resin articles so as to reinforce the articles with decrease of weight. Those glass bubbles are desired to have high compressive strength, collapse strength, or crushing strength so as to avoid being crushed or broken during injection molding or press molding of the articles. Further, glass bubbles are required to have high adhesive strength for plastic resin so as to reinforce the plastic resin articles.
U.S. Pat. Nos. 4,391,646 and 4,983,550 disclose those glass bubbles. Although the known glass bubbles disclosed in the U.S. Patents have compressive strength improved, they are still insufficient in the compressive strength and have tendency to be broken during molding of the plastic resin articles.
Further, the known glass bubbles are not good in water resistance. In detail, alkali is leached from the glass bubbles so that the adhesive strength is not sufficient for the plastic resin.